(1) Field of the Invention
The present invention relates to a terminal apparatus used in a terminal station in a data communication system.
The terminal apparatus according to the present invention is, in particular, applicable in an unmanned terminal station.
(2) Description of the Related Art
Unmanned stations, wherein data is collected and the collected data is sent to another station, are used, for example, in the following system:
in a fire information network system for detecting and reporting an occurrence of a fire;
in a fuel gas supplying system for monitoring a gas flow rate at a plurality of flow rate monitoring points;
in an electric power supplying system for monitoring an operation at a dam, an electric transformer substation, or the like.
In unmanned stations in the above systems, data is collected in each terminal station, and then is sent to a center or master station.
FIGS. 1A and 1B each show a system wherein data is collected at each terminal station, and then is sent to a master station.
In FIG. 1A, reference numeral 11 denotes a master station, 12-1 to 12-n each denote a terminal station, and 13 denotes a transmission line.
In FIG. 1B, reference numeral 21 denotes a master station, 22 denotes a terminal station, and 23 denotes a transmission line.
In both arrangements of FIGS. 1A and 1B, each terminal station collects data, and sometimes processes the collected data.
On the other hand, the master station sends a command requesting data to the corresponding terminal station(s) through the transmission line.
Responding to the command, the terminal station sends the collected and processed data to the master station through the transmission line. Thus, the master station can monitor the data collected at all of the terminal stations in the system.
The aforementioned fire information network system or the system for monitoring a gas flow rate correspond to the arrangement shown in FIG. 1A, and the aforementioned electric power supplying system wherein operations at a remote place are monitored at a master station, corresponds to the arrangement shown in FIG. 1B.
In the above-mentioned systems, if a malfunction has occurred in an unmanned terminal station, an operator must be sent to the terminal station to reset an terminal apparatus in the station. In particular, when the station is far from the master station, it takes a long time to reset and restart the terminal apparatus in the station, and therefore, the monitoring and the controlling of the system is impossible until the terminal apparatus is reset by an operator.
To solve the above problem, in the prior art, another transmission system is provided between the master station and each terminal station.
FIG. 2 shows a conventional arrangement for resetting and restarting a terminal station by a master station.
In FIG. 2, reference numeral 31 denotes an apparatus of a master station, 32 denotes a terminal station, 33 denotes a data transmission line, 34 denotes a control station attached to the master station, 35 denotes a control station attached with the terminal station, and 36 denotes a control line.
In the arrangement of FIG. 2, a construction consisting of the apparatus of a master station 31, the terminal station 32, and the data transmission line 33, corresponds to the arrangement consisting of the master station 11, the transmission line 13, and each of the terminal stations 12-i (i=1 to n) in FIG. 1A, or corresponds to the arrangement consisting of the master station 21, the transmission line 23, and the terminal station 22 in FIG. 1B.
When the master station 31 detects a malfunction of the terminal station 32 through the data received from the terminal station, the master station 31 sends a reset command to the control station 34 attached to the master station 31. When the control station 34 receives the reset command from the master station 31, the control station 34 sends the reset signal to the control station 35 attached to the terminal station 32, through the control line 36. When the control station 35 receives the reset signal, the control station 35 resets the terminal station 32. Thus, the terminal station wherein a malfunction has occurred can be reset without sending an operator to the terminal station.
However, in the above arrangement, the control stations are provided only for controlling the reset operation at the terminal station, and these control stations are connected by a control line for transmitting a reset signal, therefore, a cost for constructing a system is greatly increased.
Further, generally, it is difficult to equip another line between a master station and a terminal station other than the existing transmission line, and consequently, in the above systems, a stand-by operator is necessary for an emergency case.
In addition, in some systems, renewing or replacing of a program or data stored in an unmanned terminal station, is necessary.
For example, in a fuel gas supplying system, a sensitivity of detection of a gas flow rate must be changed since an amount of fuel gas consumption varies with the season.
Therefore, in the conventional system (for example, fuel gas supplying system), renewing or replacing data or program in a terminal station is carried out manually by an operator.